I wanted to have a bit more information about how scan classes are functioning. Indeed, after some research and experimentations, my colleagues and I have noticed unexpected (from our comprehension view) behavior from how scan classes perform.
Current situation: all of our scan classes are set in “Subscription” mode (as recommended) with multiple granularity according to the type of tags. On the other hand, we have a custom module using a TagChangeListener that allows us to retrieve tag values on the fly and this works well enough.
What we want now would be to get the tag values in a synchronous way: even if the value doesn’t change, we want to get it for every fixed period of time. But currently, tagChanged() only reacts when the value changes, so that doesn’t help us anymore. I thought I could have those values by using the tag historian but no, values aren’t logged on scan class rate.
So I was wondering if there was a better way to achieve that than just simply browse and read manually tag values every time (which kind of sound as a brute force solution for me)?
Thank you in advance for your help !